Biology

Viruses, Bacteria, Protists, and Fungi

Are any bacteria visible to the naked eye?

Epulopiscium fishelsoni, which lives in the gut of the brown surgeonfish (Acanthurus nigrofuscus), is visible to naked eye. It was first identified in 1985 and mistakenly classified as a protozoan. Later studies analyzed the organism’s genetic material and proved it to be a bacterium of unprecedented size: 0.015 inches (0.38 millimeters) in diameter, or about the size of a period in a small-print book.